This invention relates to a method of forming a dental impression and dental impression materials which quickly take a set accurately conforming to dental surfaces to be recorded and also to a method of preparing a dental prosthetic by direct conforming of a dental material to the surfaces of the oral cavity and then curing the dental material with visible light.
Methods of forming dental impressions are well known as are dental impression materials that are capable of accurately reproducing the surface contours and dimensions of oral tissues required in preparing dental prostheses. Since anatomic structures and preparations for prosthetic appliances are usually undercut, preferred impression materials are elastic or rubbery, ranging from gels, such as agar or algin preparations, to elastomers, such as rubbers, silicones, and polyethers. The nonaqueous elastomers are preferred because of their extreme dimensional accuracy and their relative stability under ambient conditions. In spite of all the improvements which have characterized current dental impression materials, they are still greatly limited by clinical factors when they are used in vivo.
It is known to prepare elastomeric impression materials by taking two separate pastes (one containing a catalyst and the other containing an accelerator), placing measured amounts of each on a pad of parchment or polyethylene-coated paper and immediately mixing them with a spatula into a substantially homogeneous mass. Such impression materials must be used immediately after mixing and while curing to set is rapid, it must be timed to allow placement by fast and slow dental practitioners and because the curing time is built in, special problems cannot be controlled with any degree of accuracy by the dental practitioner. All parts of the impression polymerize at substantially the same time. Also, the act of mixing tends to introduce air bubbles into the viscous pastes and these bubbles are difficult to eliminate, tending to cause surface imperfections in the finished impression or to distort the impression. Mixing is inconvenient and a source of inconsistency.
In the usual practice, a dental practitioner places the mixed paste in juxtaposition to the dental tissues, using either a supporting tray to contain the paste or a combination of a placement syringe and a supporting tray. The dental practitioner or dentist and the patient then wait, sometimes for ten minutes, for the polymerization reaction to progress to completion and the material to become sufficiently elastic so that the impression may be removed from the tissue without distortion of the remembered shape or form. The rate of faulty impressions is quite high due to the patient's natural tendency to move during this time, and a gagging reflex is common. The dental practitioner loses valuable time while he is thus inactivated, plus time needed for the often required retakes.
Materials commonly used for taking impressions are polysiloxanes such as described in U.S. Pat. No. 3,950,300, polyethers such as described in U.S. Pat. No. 3,453,242, and other elastomeric materials having properties more fully described in American Dental Association Specification 19.